CAREER: Understanding past and present biogeochemical cycle of potassium (K) and its implications for the global carbon cycle: proxy development based on stable K isotopes

The weathering of silicate rocks is an important part of Earth’s natural “thermostat.” Silicate weathering can scrub carbon dioxide out of the atmosphere and is considered a natural feedback that can counter the rise in global temperatures, thus maintaining a habitable climate. The analysis of the potassium (K) isotopes in silicate rocks has been closely linked to understanding past silicate weathering rates. However, recent research suggests that formation of new silicate clay minerals from the byproducts of silicate weathering may reverse the chemical reactions of silicate weathering thus making the processes less effective in cooling the planet. The formation of clays from byproducts, a process termed “reverse weathering”, is challenging to study as it occurs in remote sectors of the deep ocean and the reaction rates are slow. Thus, this presents a fundamental knowledge gap in our understanding of the long-term silicate and carbon cycles impacting what we know about past, present, and future climate. This project develops stable potassium isotopes as a novel proxy, or tracer, to help quantify modern and past silicate weathering rates. Via analyzing potassium isotopes in Earth materials, this project investigates the modern and past potassium cycle and its relationship to silicate weathering and the global carbon cycle. The study will quantify changes in marine potassium isotopes, helping to provide robust estimates on the global significance of marine clay formation and its impact on climate. Through a comprehensive plan integrating research and education, this project (1) supports geochemistry infrastructure to fulfill research and education missions of the university; (2) provides laboratory training for undergraduate and graduate students along with educational opportunities for primary and secondary students; (3) extends accessibility of a modern geochemical laboratory beyond the campus boundary to attract and build a diversified workforce in geochemistry-related fields; and (4) raises public awareness of the societal relevance of geochemistry research and of the environment and climate of our planet.The research aims to advance understanding of the marine stable potassium (K) isotopic cycle to develop a robust proxy for silicate weathering. This project applies controlled laboratory experiments and analysis of purposefully selected natural marine samples to constrain key uncertainties in the modern marine potassium isotopic cycle, including potassium isotope fractionation during seawater–basalt alterations and clay formation. Isotope mass balance models are being applied to quantitatively estimate the global significance of present-day clay formation or reverse weathering. Additionally, laboratory experiments, supplemented by spectroscopic characterization and a modeling approach, will advance knowledge on potassium isotope exchange kinetics and fractionation pertinent to derivation of seawater potassium isotope compositions from relevant geologic archives such as marine evaporites. Deliverables include development of an interpretative framework that will enable the use of geological archives to reconstruct potassium isotope signatures in ancient oceans and to assess their implications to the long-term carbon cycle. Through the integration of research and education, this project advances interdisciplinary research in potassium isotopes and expands application of the developing tool to the complex plant–soil–climate feedbacks in the context of changing climate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.